update adding demo app,

03_source/mobile/src/pages/store/CartStore.js

@@ -0,0 +1,27 @@
+import { Store } from "pullstate";
+
+const CartStore = new Store({
+    
+    cart: []
+});
+
+export default CartStore;
+
+export const addToCart = product => {
+
+    const currentCart = CartStore.getRawState().cart;
+    const added = !currentCart.includes(product);
+
+    CartStore.update(s => {
+
+        if (currentCart.includes(product)) {
+            
+            s.cart = currentCart.filter(current => current !== product);
+        } else {
+            
+            s.cart = [ ...s.cart, product ];
+        }
+    });
+
+    return added;
+}